This invention relates generally to heating fused salt baths, and more particularly to a method and apparatus for electrically heating a fused salt bath that will prevent damage to the electrical element caused by over-heating.
One conventional device for use in heating fused salt baths is shown and described in U.S. Pat. No. 4,016,403. These types of devices include a plurality of spacer elements which support electrical resistance wire elements. The spacers and wire elements are enclosed in a metal protective shell for protection against corrosive action of the bath.
This type of heater does have one serious drawback in certain environments where the bath tends to encrust on the outside of the tube casing. In such instances the encased material acts as an insulator, inhibiting heat transfer from the heating element to the bath. As the crust builds up the amount of such inhibiting of heat flow builds up. The increased insulation has two results. First, the inside of the sleeve gets hotter during any given cycle of operation, and second, a longer cycle of operation is needed to effect heat transfer from the element to the bath. These conditions can, and in fact, do cause premature failure by burn-out of the electrical elements due to over-heating.